About the KDP Margin Calculator
Margins keep your text out of the binding and away from the trimmed edge. KDP enforces minimums and rejects interiors that break them, but the inside margin (the gutter) is not a single number: thicker books curve more at the spine, so the gutter grows with page count.
This calculator looks up the minimum inside margin for your page count, the minimum outside margin for your bleed setting, and suggests slightly larger recommended values that read more comfortably. Enter your own margins to get a clear pass or fail for each, along with the live text area left on the page.
The full gutter table from KDP's guidelines is shown under the results with your book's row labelled, so you can see how close you are to the next step. A book that grows from 290 to 310 pages during editing moves up a step and needs a wider gutter.
How It Works
Inside margin minimums step up with page count: 0.375" up to 150 pages, 0.5" up to 300 pages, 0.625" up to 500 pages, 0.75" up to 700 pages, 0.875" up to 828 pages.
Outside margins (top, bottom and outside edge) must be at least 0.25" without bleed and 0.375" with bleed.
Recommended values add a buffer above the minimum. The live area is the trim size minus your inside and outside margins, and minus the top and bottom margins.
Formula
- Live width
- Live width = Trim width − Inside margin − Outside margin
- Live height
- Live height = Trim height − 2 × Outside margin
- Recommended inside
- Recommended = Minimum inside + 0.25"
Example
A 320-page 6" × 9" paperback without bleed
- 320 pages falls in the 301 to 500 row, so the minimum gutter is 0.625".
- Without bleed, the minimum outside margin is 0.25".
- Recommended: 0.875" inside and 0.5" outside, leaving a 4.625" × 8" live area.
- If you set a 0.5" inside margin, it fails: below the 0.625" minimum for this page count.
Use at least 0.625" inside and 0.25" outside; 0.875" and 0.5" give a more comfortable page.
Important Notes
- Minimums are from KDP's margin guidelines and stored as configurable values.
- Hardcovers use the same minimum table. Their tighter binding makes a slightly larger gutter a good idea.
- Headers, footers and page numbers count as content and must also sit inside the margins.
- Mirror margins (inside and outside) in your layout software so the gutter alternates correctly between left and right pages.
Frequently Asked Questions
What is the gutter?
The gutter is the inside margin, next to the spine. It needs to be larger than the outside margin because pages curve into the binding.
Why does the gutter depend on page count?
Thicker books do not open as flat, so more of each page disappears into the spine. KDP increases the minimum gutter in steps as the page count rises.
Why is the outside margin bigger with bleed?
Books with bleed are trimmed after printing, and the trim can vary slightly. The larger 0.375" minimum keeps text safely away from the cut.
Are the recommended margins required?
No. Only the minimums are required. The recommendations give more breathing room, which most readers find easier on the eye.
Do margins apply to images too?
Text and important image details must stay inside the margins. Artwork that is meant to run off the page edge is allowed into the bleed area only when your interior is set up with bleed.
Related KDP Tools
- KDP Trim Size CalculatorCompare KDP trim sizes, convert units and see regular vs large trim pricing.
- KDP Bleed CalculatorCalculate interior page size with bleed for full-page images and backgrounds.
- KDP Page Count CalculatorConvert word count to estimated pages, or pages to words, by trim and font size.
- KDP Cover Size CalculatorGet full-wrap cover dimensions with a live back, spine and front diagram.
- KDP Spine Width CalculatorCalculate paperback spine width from page count and paper type.
- Image DPI CheckerRead pixel size, DPI metadata, print size and file details from an image.
Related Guides
- KDP Trim Sizes ExplainedEvery standard KDP trim size in inches and mm, the regular vs large trim rule and how it affects print cost, common sizes by genre, and how custom sizes work.
- KDP Bleed ExplainedWhat bleed is, KDP's 0.125" (3.2 mm) bleed requirement, how to size interior pages and covers with bleed, safe margins, and when your book needs bleed at all.